Alloyed steel powder for powder metallurgy, iron-based mixed powder for powder metallurgy, and sintered body

ABSTRACT

Provided is an alloyed steel powder for powder metallurgy which has excellent compressibility and can be used to produce a sintered body that obtains improved strength simply by sintering. The alloyed steel powder for powder metallurgy contains Cu: 1.0 mass % or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass % or less, and at least one selected from the group consisting of V: 0.05 mass % or more and 0.50 mass % or less, Nb: 0.02 mass % or more and 0.40 mass % or less, and Ti: 0.02 mass % or more and 0.40 mass % or less, with the balance consisting of Fe and inevitable impurities.

TECHNICAL FIELD

This disclosure relates to an alloyed steel powder for powdermetallurgy, an iron-based mixed powder for powder metallurgy, and asintered body.

BACKGROUND

Powder metallurgical techniques enable producing parts with complicatedshapes in shapes that are extremely close to product shapes (so-callednear net shapes) with high dimensional accuracy, and consequentlysignificantly reducing machining costs during the production of parts.Therefore, powder metallurgical products are widely used as all kinds ofparts for machines. Further, to cope with demands for reductions in sizeand weight and increasing complexity of parts, requirements for powdermetallurgical techniques are becoming more stringent.

Against this background, requirements for alloyed steel powders used inpowder metallurgy are also becoming more stringent, and it is requiredthat the alloyed steel powders have good compressibility and sinteredbodies obtained by sintering the alloyed steel powders have excellentmechanical properties. Further, a reduction in production costs isstrongly required. From such a viewpoint, it is desired that the alloyedsteel powders can be produced by conventional metallurgical powderproduction processes without any additional step, and that the alloyedsteel powders do not need to contain any expensive alloy component suchas Ni.

For example, the following methods have been proposed to improve thestrength of a sintered body: a method of mixing a steel powder with aspecific metal powder to obtain a mixed powder, a method ofdiffusionally adhering a specific metal powder to the surface of a steelpowder, a method of further combining with graphite powder, and a methodof using an alloyed steel powder that has been alloyed with a specificmetal element.

For example, JP2012520942A (PTL 1) proposes a steel powder alloyed withV and Mn, which may be mixed with Cu and Ni powders.

WO2016092827A (PTL 2) proposes an alloyed steel powder for powdermetallurgy in which a Cu powder is diffusionally adhered to the surfaceof a steel powder alloyed with Cu.

JP2003500538A (PTL 3) proposes a mixed powder for powder metallurgy inwhich a steel powder alloyed with Mo is mixed with either or both of aCu powder and a Ni powder.

JP2010529302A (PTL 4) proposes an alloyed steel powder alloyed with Ni,Mo and Mn.

JP2013508558A (PTL 5) proposes a method of binding graphite powder to aniron-based powder by a binder, where the iron-based powder may bealloyed with alloying elements such as Ni, Cr, Mo and Mn.

JP2013204112A (PTL 6) proposes a method of combining alloying elementssuch as Cr, Mo and Cu with a reduced amount of C.

CITATION LIST Patent Literature

-   PTL 1: JP2012520942A-   PTL 2: WO2016092827A-   PTL 3: JP2003500538A-   PTL 4: JP2010529302A-   PTL 5: JP2013508558A-   PTL 6: JP2013204112A

SUMMARY Technical Problem

However, in PTL 1, the effect of improving the strength of a sinteredbody by precipitation strengthening of V is limited even if a Cu powderor the like is used as well. Further, containing Mn may cause a decreasein the strength of a sintered body due to oxidation, and furtherimprovement in strength is required.

In PTL 2, the effect of improving the strength of a sintered body by theuse of Cu alone is limited, and further improvement in strength isrequired.

In PTL 3, the effect of improving the strength of a sintered body byalloying of Mo is limited even if a Cu powder or the like is used aswell, and further improvement in strength is required.

In PTL 4, containing Ni leads to a high cost, and containing Mn maycause a decrease in the strength of a sintered body due to oxidation.

In PTL 5, it is necessary to perform heat treatment such as carburizing,quenching and tempering after sintering to improve the mechanicalproperties of a sintered body.

PTL 6 only improves the compressibility of a mixed powder by reducingthe amount of C (graphite powder or the like) to be mixed with analloyed steel powder, which cannot improve the compressibility of thealloyed steel powder itself. Further, it is necessary to set the coolingrate in quenching after sintering to 2° C./s or higher to ensure thehardness and tensile strength of a sintered body. To control the coolingrate as above, it is necessary to modify production apparatus, whichincreases production costs.

It could thus be helpful to provide an alloyed steel powder for powdermetallurgy which has excellent compressibility and can be used toproduce a sintered body that obtains improved strength simply bysintering (without further heat treatment). As used herein, thecompressibility refers to the density (compressed density) of a formedbody obtained by performing pressing at a given pressure, and the valueis preferably as high as possible.

It is also helpful to provide an iron-base mixed powder for powdermetallurgy containing the above-described alloyed steel powder forpowder metallurgy.

Further, it is helpful to provide a sintered body using theabove-described alloyed steel powder for powder metallurgy or theabove-described iron-based mixed powder for powder metallurgy.

Solution to Problem

As a result of diligent studies, we found that an alloyed steel powderusing Cu, Mo, and at least one of V, Nb and Ti, each in a specificamount, as alloying elements has excellent compressibility and can beused to provide a sintered body that obtains improved strength simply bysintering, thereby completing the present disclosure. The alloyed steelpowder of the present disclosure can uniformize the distribution of Cuand Mo, which in turn can uniformize the distribution of Cu and Mo inthe sintered body. Further, because at least one of V, Nb and Ti iscontained, precipitates in the sintered body are refined, andconsequently, the microstructure can be refined. It is presumed that allthese factors can lead to a sintered body with improved strength.

We thus provide the following.

[1] An alloyed steel powder for powder metallurgy, comprising(consisting of)

Cu: 1.0 mass % or more and 8.0 mass % or less,

Mo: more than 0.50 mass % and 2.00 mass % or less, and

at least one selected from the group consisting of V: 0.05 mass % ormore and 0.50 mass % or less, Nb: 0.02 mass % or more and 0.40 mass % orless, and Ti: 0.02 mass % or more and 0.40 mass % or less,

with the balance consisting of Fe and inevitable impurities.

[2] The alloyed steel powder for powder metallurgy according to [1],comprising V: 0.05 mass % or more and 0.50 mass % or less.

[3] The alloyed steel powder for powder metallurgy according to [1] or[2], comprising Nb: 0.02 mass % or more and 0.40 mass % or less.

[4] The alloyed steel powder for powder metallurgy according to any oneof [1] to [3], comprising Ti: 0.02 mass % or more and 0.40 mass % orless.

[5] An iron-based mixed powder for powder metallurgy, comprising thealloyed steel powder for powder metallurgy according to any one of [1]to [4] and a metal powder, wherein

the metal powder is either or both of a Cu powder of more than 0 mass %and 4 mass % or less and a Mo powder of more than 0 mass % and 4 mass %or less with respect to 100 mass % of the iron-based mixed powder forpowder metallurgy.

[6] A sintered body using the alloyed steel powder for powder metallurgyaccording to any one of [1] to [4] or the iron-base mixed powder forpowder metallurgy according to [5].

Advantageous Effect

The alloyed steel powder for powder metallurgy of the present disclosurehas excellent compressibility and can be used to provide a sintered bodythat obtains improved strength simply by sintering.

In addition, the alloyed steel powder for powder metallurgy of thepresent disclosure is advantageous in that it does not contain alloyingelements that are easily oxidized, such as Cr and Mn, and thus does notcause a decrease in strength of a sintered body due to oxidation ofalloying elements.

Further, the alloyed steel powder for powder metallurgy of the presentdisclosure does not contain elements such as Ni, which causes a highalloy cost, or Cr, which requires annealing in a special atmosphere, andit does not require additional production processes such as coating orplating. Therefore, it is advantageous in terms of cost and is alsoconvenient in that it can be produced by conventional metallurgicalpowder production processes.

The iron-based mixed powder for powder metallurgy of the presentdisclosure also has excellent compressibility and can be used to providea sintered body that obtains improved strength simply by sintering.

By using the alloyed steel powder for powder metallurgy or theiron-based mixed powder for powder metallurgy of the present disclosure,it is possible to produce a sintered body with improved strength at alow cost.

DETAILED DESCRIPTION

The following describes embodiments of the present disclosure in detail.

[Alloyed Steel Powder for Powder Metallurgy]

The alloyed steel powder for powder metallurgy of the present disclosure(hereinafter also referred to as “alloyed steel powder”) containsiron-based alloy in which Cu, Mo, and at least one of V, Nb and Ti arecontained as essential components. As used herein, the “iron-based”means containing 50 mass % or more of Fe. In the description of thechemical composition, “%” denotes “mass %” unless otherwise noted. Thecontent of the chemical composition of the alloyed steel powder forpowder metallurgy is an amount with respect to 100 mass % of the alloyedsteel powder for powder metallurgy.

Cu: 1.0% or More and 8.0% or Less

Cu is an element that improves hardenability, and Cu is superior toelements such as Si, Cr and Mn in that it is more resistant tooxidation. Cu is also advantageous in that it is cheaper than Ni. Whenthe Cu content is less than 1.0%, the effect of improving hardenabilityby Cu is insufficient. Therefore, the Cu content is set to 1.0% or more.On the other hand, sintering is generally performed at about 1130° C.during the production of sintered bodies. According to the Fe—Cu phasediagram, when the Cu content exceeds 8.0%, Cu precipitates in theaustenite phase. The Cu precipitates formed during sintering do notfunction effectively to improve hardenability, but rather remain as asoft phase in the microstructure, which may lead to deterioration ofmechanical properties. Therefore, the Cu content is set to 8.0% or less.When Cu is added within the above range, it is possible to sufficientlyimprove tensile strength while suppressing a decrease in density. Toeffectively obtain a higher strength, the Cu content is preferably 2.0%or more. The Cu content is preferably 6.0% or less.

Mo: More than 0.50% and 2.00% or Less

Mo is an element that improves hardenability, and Mo is superior toelements such as Si, Cr and Mn in that it is more resistant tooxidation. Further, Mo has a characteristic that a small amount ofaddition, which is less than that of Ni, is sufficient for obtaining aneffect of improving hardenability. When the Mo content is 0.50% or less,the strength-improving effect of Mo is insufficient. Therefore, the Mocontent is set to more than 0.50%. On the other hand, when the Mocontent exceeds 2.00%, the compressibility of the alloyed steel powderdecreases, and a die for pressing is easily worn out. In addition, theeffect of increasing the strength of a sintered body by containing Mo issaturated. Therefore, the Mo content is set to 2.00% or less. Toeffectively obtain a higher strength, the Mo content is preferably 1.00%or more. The Mo content is preferably 1.50% or less.

The alloyed steel powder of the present disclosure contains at least oneof V, Nb and Ti. The alloyed steel powder may contain only one of V, Nband Ti, two of them, or all three of them. When two of them arecontained, it may be any combination of V and Nb, V and Ti, or Nb andTi. The content of each of V, Nb and Ti is as follows.

V: 0.05% or More and 0.50% or Less

V is an element that acts extremely effectively to improve strength byprecipitating as carbides in a solid portion of a sintered body. Whenthe V content is less than 0.05%, the amount of carbides formed isinsufficient, and the strength of a sintered body cannot be sufficientlyimproved. Therefore, when V is contained, the V content is set to 0.05%or more. On the other hand, when the V content exceeds 0.50%, thecarbides are coarsened, which deteriorates the strength-improvingeffect, and each particle of the alloyed steel powder is hardened, whichcauses a decrease in compressibility. Further, it also isdisadvantageous from an economic viewpoint. Therefore, the V content isset to 0.50% or less. To effectively obtain a higher strength, the Vcontent is preferably 0.10% or more. The V content is preferably 0.40%or less.

Nb: 0.02% or More and 0.40% or Less

Nb is an element that not only greatly enhances hardenability but alsoacts effectively to improve strength by precipitating as carbides in asolid portion of a sintered body. When the Nb content is less than0.02%, the amount of carbides formed is insufficient, and the strengthof a sintered body cannot be sufficiently improved. Therefore, when Nbis contained, the Nb content is set to 0.02% or more. On the other hand,when the Nb content exceeds 0.40%, the carbides are coarsened, whichdeteriorates the strength-improving effect, and each particle of thealloyed steel powder is hardened, which causes a decrease incompressibility. Further, it also is disadvantageous from an economicviewpoint. Therefore, when Nb is contained, the Nb content is set to0.40% or less. When Nb is contained, the Nb content is preferably 0.05%or more to effectively obtain a higher strength. The Nb content ispreferably 0.20% or less to effectively obtain a higher strength.

Ti: 0.02% or More and 0.40% or Less

Ti is an element that acts effectively to improve strength byprecipitating as carbides in a solid portion of a sintered body. Whenthe Ti content is less than 0.02%, the amount of carbides formed isinsufficient, and the strength of a sintered body cannot be sufficientlyimproved. Therefore, when Ti is contained, the Ti content is set to0.02% or more. On the other hand, when the Ti content exceeds 0.40%, thecarbides are coarsened, which deteriorates the strength-improvingeffect, and each particle of the alloyed steel powder is hardened, whichcauses a decrease in compressibility. Further, it also isdisadvantageous from an economic viewpoint. Therefore, when Ti iscontained, the Ti content is set to 0.40% or less. When Ti is contained,the Ti content is preferably 0.05% or more to effectively obtain ahigher strength. The Ti content is preferably 0.20% or less toeffectively obtain a higher strength.

The balance of the alloyed steel powder other than the aforementionedcomponents consists of Fe and inevitable impurities. The amount ofinevitable impurities is not particularly limited as long as it is anamount inevitably mixed in. However, it is preferable to controlinevitable impurities so that they are substantially not contained.Because Ni causes an increase in alloy costs, it is preferable tocontrol the Ni content to 0.1% or less. Because Cr is easily oxidizedand it requires control of annealing atmosphere, it is preferable tocontrol the Cr content to 0.1% or less. For the same reason as for Cr,it is preferable to control the Si content to 0.1% or less. It ispreferable to suppress C to 0.01% or less, 0 to 0.20% or less, Mn to0.15% or less, P to 0.025% or less, S to 0.025% or less, N to 0.05% orless, and other elements to 0.01% or less.

The alloyed steel powder of the present disclosure includes thefollowing embodiments.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, and V: 0.05 mass % or more and 0.50 mass % or less, with thebalance consisting of Fe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, and Nb: 0.02 mass % or more and 0.40 mass % or less, with thebalance consisting of Fe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, Ti: 0.02 mass % or more and 0.40 mass % or less, with thebalance consisting of Fe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, V: 0.05 mass % or more and 0.50 mass % or less, and Nb: 0.02mass % or more and 0.40 mass % or less, with the balance consisting ofFe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, V: 0.05 mass % or more and 0.50 mass % or less, and Ti: 0.02mass % or more and 0.40 mass % or less, with the balance consisting ofFe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, Nb: 0.02 mass % or more and 0.40 mass % or less, and Ti: 0.02mass % or more and 0.40 mass % or less, with the balance consisting ofFe and inevitable impurities.

An alloyed steel powder for powder metallurgy containing Cu: 1.0 mass %or more and 8.0 mass % or less, Mo: more than 0.50 mass % and 2.00 mass% or less, V: 0.05 mass % or more and 0.50 mass % or less, Nb: 0.02 mass% or more and 0.40 mass % or less, and Ti: 0.02 mass % or more and 0.40mass % or less, with balance consisting of Fe and inevitable impurities.

The method of producing the alloyed steel powder is not particularlylimited, and the alloyed steel powder may be produced with any method.For example, the alloyed steel powder may be an atomized powder producedwith an atomizing method, and it is preferably a water atomized powderproduced with a water atomizing method, which causes low productioncosts and is easy for mass production. In the case of producing thealloyed steel powder with an atomizing method, the alloyed steel powdercan be obtained by, for example, atomizing molten steel, which has beenadjusted to have the predetermined chemical composition, to obtain apowder, and reducing and/or classifying the powder as necessary.

The particle size of the alloyed steel powder is not particularlylimited, and the alloyed steel powder may have any particle size. Fromthe viewpoint of ease of production, it is preferable to have an averageparticle size of 30 μm or more and 150 μm or less. An alloyed steelpowder having an average particle size within the above range can beproduced industrially at low costs with a water atomizing method. Asused here, the average particle size refers to the mass-based mediansize (D50). The average particle size can be determined by interpolationas a particle size for which a value of 50% is reached when calculatingthe mass-based cumulative particle size distribution from particle sizedistribution measured with the dry sieving method described in JIS Z2510.

[Iron-Based Mixed Powder for Powder Metallurgy]

The alloyed steel powder can be used for powder metallurgy as it is, orit can be used as an iron-based mixed powder for powder metallurgycontaining the alloyed steel powder and a metal powder (hereinafter alsoreferred to as “mixed powder”). The metal powder in the mixed powder ofthe present disclosure is either or both of a Cu powder: more than 0%and 4% or less, and a Mo powder: more than 0% and 4% or less. Thecontent of the chemical composition of the iron-based mixed powder forpowder metallurgy is an amount with respect to 100 mass % of theiron-based mixed powder for powder metallurgy.

Cu Powder: More than 0% and 4% or Less

A Cu powder can be added to the alloyed steel powder to promotesintering and improve strength. However, when it exceeds 4%, the amountof liquid phase formed during sintering increases, which decreases thedensity of a sintered body due to expansion and deteriorates thestrength. Therefore, the amount of Cu powder added is set to 4% or less.When a Cu powder is added, it is preferably 0.5% or more to effectivelyimprove the strength.

Mo Powder: More than 0% and 4% or Less

A Mo powder can be added to the alloyed steel powder to promotesintering and improve strength. However, when it exceeds 4%, the alloyedsteel powder is hardened, which decreases the compressive density anddeteriorates the strength. Therefore, the amount of Mo powder added isset to 4% or less. When a Mo powder is added, it is preferably 0.5% ormore to effectively improve the strength.

The method of producing the mixed powder is not particularly limited,and the mixed powder may be produced with any method. For example, itcan be produced by mixing either or both of the Cu and Mo powders of thecontents described above with the alloyed steel powder. The mixing canbe performed with any method. Examples thereof include methods of mixingusing a V-shaped mixer, a double cone mixer, a Henschel Mixer, or aNauta Mixer. During the mixing, a binder such as a machine oil may beadded to prevent segregation of either or both of the Cu and Mo powders.Alternatively, the mixed powder may be obtained by filling the alloyedsteel powder, and either or both of the Cu and Mo powders of thecontents described above in a mold for pressing.

[Sintered Body]

The present disclosure also relates to a sintered body obtained bysintering a formed body containing the alloyed steel powder or the mixedpowder.

The sintered body may be produced using the alloyed steel powder or themixed powder (hereinafter also referred to as “raw material”) as a rawmaterial. The method of producing the sintered body is not particularlylimited, and the sintered body may be produced with any productionmethod. For example, the sintered body can be produced by adding anyoptional component as required to the raw material, and subjecting themto pressing and then sintering.

[Optional Component]

The raw material of the sintered body may be the raw material as it is,or may also include an auxiliary raw material such as a carbon powder.

The carbon powder is not particularly limited and is preferably graphitepowder (natural graphite powder, artificial graphite powder, etc.) orcarbon black. The addition of carbon powder can further improve thestrength of the sintered body. When a carbon powder is added, the carbonpowder is preferably 0.2 parts by mass or more with respect to 100 partsby mass of the raw material in terms of the strength-improving effect.The carbon powder is preferably 1.2 parts by mass or less with respectto 100 parts by mass of the raw material.

A lubricant may be added to the raw material. Containing a lubricantfacilitates the extraction of a formed body from a press mold. Thelubricant is not particularly limited, and examples thereof includemetal soap (zinc stearate, lithium stearate, etc.) and amide-based wax(ethylene bis-stearate amide, etc.). The lubricant is preferably inpowder form. When a lubricant is used, the lubricant is preferably 0.3parts by mass or more with respect to 100 parts by mass of the rawmaterial. The lubricant is preferably 1.0 part by mass or less withrespect to 100 parts by mass of the raw material.

A machinability-improving powder may be added to the raw material. Themachinability-improving powder is not particularly limited, and examplesthereof includes a MnS powder and an oxide powder. When amachinability-improving powder is used, the machinability-improvingpowder is preferably 0.1 parts by mass or more with respect to 100 partsby mass of the raw material. The machinability-improving powder ispreferably 0.7 parts by mass or less with respect to 100 parts by massof the raw material.

(Pressing)

The raw material is blended with optional components such as anauxiliary raw material, a lubricant, and a machinability-improvingpowder as required and then subjected to pressing to obtain a formedbody in a desired shape. The method of pressing is not particularlylimited, and any method may be used. Examples thereof include a methodof filling a press mold with the raw material and the like andperforming pressing. A lubricant may be applied or adhered to the pressmold. In this case, the amount of the lubricant is preferably 0.3 partsby mass or more with respect to 100 parts by mass of the raw material.The amount of the lubricant is preferably 1.0 part by mass or less withrespect to 100 parts by mass of the raw material.

The pressure at which pressing is performed to obtain a formed body maybe set to 400 MPa or more and 1000 MPa or less. Within this range, thedensity of the formed body is lowered, the density of the sintered bodyis reduced, an insufficient strength can be avoided, and burden on thepress mold can also be suppressed. The raw material of the presentdisclosure can be pressed under a pressure of 588 MPa to obtain a formedbody with a density (compressed density) of 6.75 Mg/m³ or more, forexample. The density (compressed density) of the formed body ispreferably 6.80 Mg/m³ or more.

(Sintering)

The resulting formed body is then sintered. The method of sintering isnot particularly limited and can be any method. The sinteringtemperature may be 1100° C. or higher and is preferably 1120° C. orhigher from the viewpoint of performing sintering sufficiently. On theother hand, the distribution of Cu and Mo becomes uniform in thesintered body as the sintering temperature increases, so that the upperlimit of the sintering temperature is not particularly limited. However,the sintering temperature is preferably 1250° C. or lower and morepreferably 1180° C. or lower from the viewpoint of controlling theproduction costs. Because the raw material is an alloyed steel powderobtained by alloying Cu, Mo and at least one of V, Nb and Ti, thedistribution of Cu and Mo can be made uniform even at a sinteringtemperature within the above range. As a result, the strength of thesintered body can be effectively improved.

The sintering time may be 15 minutes or longer and 50 minutes orshorter. Within this range, insufficient sintering and insufficientstrength can be avoided, and the production costs can be suppressed. Thecooling rate during cooling after sintering may be 20° C./min or higherand 40° C./min or lower. At a cooling rate of lower than 20° C./min,quenching cannot be performed sufficiently, and the tensile strength maybe reduced. A cooling rate of 40° C./min or higher requires ancillaryequipment to accelerate the cooling rate, which increases the productioncosts.

In the case of using a lubricant, a degreasing process may be added inwhich the formed body is held in a temperature range of 400° C. orhigher and 700° C. or lower for a certain period of time to decomposeand remove the lubricant before sintering.

The conditions and equipment for the production of the sintered bodyother than the above are not particularly limited and may be anycommonly known ones, for example.

The resulting sintered body may be subjected to treatment such ascarburizing-quenching and tempering.

EXAMPLES

More detailed description of the present disclosure is given below basedon examples. The following examples merely represent preferred examplesof the present disclosure, and the present disclosure is not limited tothese examples.

Alloyed steel powders and sintered bodies using the alloyed steelpowders were produced by the following procedures in the examples.

Production of Alloyed Steel Powder

Molten steels were adjusted to have the chemical compositions listed inTable 1 to Table 4, and alloyed steel powders were prepared with a wateratomizing method. The amounts of Si, Mn, P, S and Cr contained in thealloyed steel powder as inevitable impurities were as follows: Si: lessthan 0.05 mass %, Mn: less than 0.15 mass %, P: less than 0.025 mass %,S: less than 0.025 mass %, and Cr: less than 0.03 mass %.

Each of the resulting alloyed steel powder was held at 920° C. in ahydrogen atmosphere for 30 minutes for finish-reduction. Afterfinish-reduction, a heat-treated body, in which particles were sinteredtogether to form a lump, was ground using a hammer mill and classifiedusing a sieve with a mesh size of 180 μm, and the powder under the sievewas collected and used as an alloyed steel powder. The amounts of C, Oand N contained in the alloyed steel powder as inevitable impuritieswere as follows: C: less than 0.01 mass %, O: less than 0.20 mass %, andN: less than 0.05 mass %. The chemical composition of the alloyed steelpowder was equivalent to the chemical composition of the molten steelabove.

Production of Diffusionally Adhered Alloy Steel Powder

A Cu powder (D50 of about 30 μm) or an oxidized Mo powder (D50 of about3 μm) was added to the alloyed steel powder in such an amount that thecontent of Cu or Mo in a diffusionally adhered alloy steel powder wasthe value listed in Table 1 to Table 3, and the powders were mixed in aV-shaped mixer for 15 minutes and then held at 920° C. in a hydrogenatmosphere for 30 minutes for finish-reduction. After finish-reduction,a reduced body, in which particles were sintered together to form alump, was ground using a hammer mill and classified using a sieve with amesh size of 180 μm, and the powder under the sieve was collected andused as a diffusionally adhered alloy steel powder to which Cu or Mo wasdiffusionally adhered. The amounts of C, O and N contained in thediffusionally adhered alloy steel powder as inevitable impurities wereas follows: C: less than 0.01 mass %, O: less than 0.20 mass %, and N:less than 0.05 mass %.

Production of Sintered Body

The alloyed steel powder or diffusionally adhered alloy steel powder wasadded with 0.8 parts by mass of graphite powder, 0.6 parts by mass of alubricant (zinc stearate), and a Cu powder (D50 of about 45 μm) or a Mopowder (D50 of about 25 μm) in an amount listed in Tables 1 to 3 or 5with respect to 100 parts by mass of the alloyed steel powder ordiffusionally adhered alloy steel powder, and the powders were mixedusing a double-cone mixer to obtain an iron-based mixed powder. Theiron-based mixed powder was pressed into a rectangular shape of 10 mm×10mm×55 mm at a pressing pressure of 588 MPa to obtain a formed body. Thedensity of the formed body was calculated by dividing the weight of theformed body by the volume of the rectangular body.

The formed body was held at 1130° C. for 20 minutes in a 10% H₂-90% N₂atmosphere to obtain a sintered body. A test piece having a length of 50mm and a diameter of 3 mm was cut out from the sintered body, and themaximum stress before breaking (tensile strength) was measured.

Example 1

This is an example relating to an alloyed steel powder in which Cu, Moand V are added. Table 1 lists the chemical composition and theevaluation results. In the chemical composition, “—” means that thecomponent is not added, and the same applies to the followingdescription.

Iron-based powders prepared under the following four sets of conditionswere also evaluated as comparative examples. In No. 1-10, Cu wasdiffusively adhered to the surface of an alloyed steel powder containingMo and V as alloying elements, and the alloyed steel powder was mixedwith graphite powder and a lubricant. In No. 1-11, an alloyed steelpowder containing Mo and V as alloying elements was mixed with a Cupowder, graphite powder and a lubricant. In No. 1-12, Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and V asalloying elements, and the alloyed steel powder was mixed with graphitepowder and a lubricant. In No. 1-13, an alloyed steel powder containingCu and V as alloying elements was mixed with a Mo powder, graphitepowder and a lubricant. Table 1 lists the amount adhered, the amountadded and the evaluation results.

As indicated in Table 1, the tensile strength was significantly improvedin No. 1-2 containing Cu, Mo and V as compared to No. 1-1 containingonly Cu and V. Compared to No. 1-2, the tensile strength of No. 1-3, inwhich no V was added and Cu was increased, was not as high as that ofNo. 1-2. The tensile strength was significantly improved in No. 1-6containing Cu, Mo and V as compared to No. 1-4 containing only Cu and Vand No. 1-5 containing only Mo and V. Compared to No. 1-6, a hightensile strength was obtained in No. 1-7 with increased Cu, No. 1-8 withincreased Mo, and No. 1-9 with increased V.

With regard to compressibility, it can be seen that Nos. 1-2 and 1-6 to1-9, which are disclosed examples, all have a sufficiently high densityand excellent compressibility. It can be seen from the results of Nos.1-5 to 1-7 that Cu can improve the tensile strength by increasing theamount added while maintaining a high density.

The sintered body of No. 1-10 using a diffusionally adhered alloy steelpowder, in which Cu was diffusively adhered to the surface of an alloyedsteel powder containing Mo and V as alloying elements, and the sinteredbody of No. 1-11 using a mixed powder obtained by mixing the samealloyed steel powder with a Cu powder were inferior to the sintered bodyof No. 1-6 in terms of tensile strength, although they had the samecontents of Cu, Mo and V. The sintered body of No. 1-12 using adiffusionally adhered alloy steel powder, in which Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and V asalloying elements, and the sintered body of No. 1-13 using a mixedpowder obtained by mixing the same alloyed steel powder with a Mo powderwere inferior to the sintered body of No. 1-6 in terms of tensilestrength, although they had the same contents of Cu, Mo and V.

TABLE 1 Metal Alloyed steel Diffusionally powder powder adhered powderAmount Sintered Chemical Amount added*³ Formed body composition *¹adhered*² (mass %) body Tensile (mass %) (mass %) Cu Mo Density strengthNo. Cu Mo V Cu Mo powder powder (Mg/m³) (MPa) Remarks 1-1 1.0 — 0.05 — —— — 7.07 461 Comparative example 1-2 1.0 0.51 0.05 — — — — 7.00 572Example 1-3 3.0 0.51 — — — — — 7.01 530 Comparative example 1-4 3.0 —0.20 — — — — 7.02 493 Comparative example 1-5 — 1.20 0.20 — — — — 6.94614 Comparative example 1-6 3.0 1.20 0.20 — — — — 6.91 770 Example 1-78.0 1.20 0.20 — — — — 6.96 765 Example 1-8 3.0 2.00 0.20 — — — — 6.81772 Example 1-9 3.0 1.20 0.50 — — — — 6.82 719 Example 1-10 — 1.20 0.203.0 — — — 6.97 612 Comparative example 1-11 — 1.20 0.20 — — 3.0 — 6.98602 Comparative example 1-12 3.0 — 0.20 — 1.20 — — 7.01 530 Comparativeexample 1-13 3.0 — 0.20 — — — 1.20 7.01 516 Comparative example *¹ Thebalance of the alloyed steel powder consists of Fe and inevitableimpunties. *²The total of the alloyed steel powder and the diffusionallyadhered powder is taken as 100 mass %. *³The total of the alloyed steelpowder and the metal powder is taken as 100 mass %.

Example 2

This is an example relating to an alloyed steel powder in which Cu, Moand Nb are added. Table 2 lists the chemical composition and theevaluation results.

Iron-based powders prepared under the following four sets of conditionswere also evaluated as comparative examples. In No. 2-11, Cu wasdiffusively adhered to the surface of an alloyed steel powder containingMo and Nb as alloying elements, and the alloyed steel powder was mixedwith graphite powder and a lubricant. In No. 2-12, an alloyed steelpowder containing Mo and Nb as alloying elements was mixed with a Cupowder, graphite powder and a lubricant. In No. 2-13, Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and Nbas alloying elements, and the alloyed steel powder was mixed withgraphite powder and a lubricant. In No. 2-14, an alloyed steel powdercontaining Cu and Nb as alloying elements was mixed with a Mo powder,graphite powder and a lubricant. Table 2 lists the amount adhered, theamount added and the evaluation results.

As indicated in Table 2, the tensile strength was significantly improvedin No. 2-2 containing Cu, Mo and Nb as compared to No. 2-1 containingonly Cu and Nb. Compared to No. 2-2, the tensile strength of No. 2-3, inwhich no Nb was added and Cu was increased, was not as high as that ofNo. 2-2. The tensile strength was significantly improved in No. 2-6containing Cu, Mo and Nb as compared to No. 2-4 containing only Cu andNb and No. 2-5 containing only Mo and Nb. Compared to No. 2-6, a hightensile strength was obtained in No. 2-7 with increased Cu, No. 2-8 withincreased Mo, and No. 2-9 with increased Nb. On the other hand, No.2-10, in which the amounts of Cu, Mo and Nb were outside the range ofthe present disclosure, had a lowered density and a deteriorated tensilestrength.

With regard to compressibility, it can be seen that Nos. 2-2 and 2-6 to2-9, which are disclosed examples, all have a sufficiently high densityand excellent compressibility. It can be seen from the results of Nos.2-5 to 2-7 that Cu can improve the tensile strength by increasing theamount added while maintaining a high density.

The sintered body of No. 2-11 using a diffusionally adhered alloy steelpowder, in which Cu was diffusively adhered to the surface of an alloyedsteel powder containing Mo and Nb as alloying elements, and the sinteredbody of No. 2-12 using a mixed powder obtained by mixing the samealloyed steel powder with a Cu powder were inferior to the sintered bodyof No. 2-6 in terms of tensile strength, although they had the samecontents of Cu, Mo and Nb. The sintered body of No. 2-13 using adiffusionally adhered alloy steel powder, in which Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and Nbas alloying elements, and the sintered body of No. 2-14 using a mixedpowder obtained by mixing the same alloyed steel powder with a Mo powderwere inferior to the sintered body of No. 2-6 in terms of tensilestrength, although they had the same contents of Cu, Mo and Nb.

TABLE 2 Metal Alloyed steel Diffusionally powder powder adhered powderAmount Sintered Chemical Amount added*³ Formed body composition *¹adhered*² (mass %) body Tensile (mass %) (mass %) Cu Mo Density strengthNo. Cu Mo Nb Cu Mo powder powder (Mg/m³) (MPa) Remarks 2-1 1.0 — 0.02 —— — — 7.06 458 Comparative example 2-2 1.0 0.51 0.02 — — — — 7.01 570Example 2-3 3.0 0.51 — — — — — 6.99 526 Comparative example 2-4 3.0 —0.10 — — — — 7.04 488 Comparative example 2-5 — 1.20 0.10 — — — — 6.97610 Comparative example 2-6 3.0 1.20 0.10 — — — — 6.92 763 Example 2-78.0 1.20 0.10 — — — — 6.98 758 Example 2-8 3.0 2.00 0.10 — — — — 6.83765 Example 2-9 3.0 1.20 0.40 — — — — 6.85 720 Example 2-10 8.1 2.100.41 — — — — 6.65 620 Comparative example 2-11 — 1.20 0.20 3.0 — — —6.97 608 Comparative example 2-12 — 1.20 0.20 — — 3.0 — 6.98 598Comparative example 2-13 3.0 — 0.20 — 1.20 — — 7.04 518 Comparativeexample 2-14 3.0 — 0.20 — — — 1.20 7.03 510 Comparative example *¹ Thebalance of the alloyed steel powder consists of Fe and inevitableimpurities. *²The total of the alloyed steel powder and thediffusionally adhered powder is taken as 100 mass %. *³The total of thealloyed steel powder and the metal powder is taken as 100 mass %.

Example 3

This is an example relating to an alloyed steel powder in which Cu, Moand Ti are added. Table 3 lists the chemical composition and theevaluation results.

Iron-based powders prepared under the following four sets of conditionswere also evaluated as comparative examples. In No. 3-11, Cu wasdiffusively adhered to the surface of an alloyed steel powder containingMo and Ti as alloying elements, and the alloyed steel powder was mixedwith graphite powder and a lubricant. In No. 3-12, an alloyed steelpowder containing Mo and Ti as alloying elements was mixed with a Cupowder, graphite powder and a lubricant. In No. 3-13, Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and Tias alloying elements, and the alloyed steel powder was mixed withgraphite powder and a lubricant. In No. 3-14, an alloyed steel powdercontaining Cu and Ti as alloying elements was mixed with a Mo powder,graphite powder and a lubricant. Table 1 lists the amount adhered, theamount added and the evaluation results.

As indicated in Table 3, the tensile strength was significantly improvedin No. 3-2 containing Cu, Mo and Ti as compared to No. 3-1 containingonly Cu and Ti. Compared to No. 3-2, the tensile strength of No. 3-3, inwhich no Ti was added and Cu was increased, was not as high as that ofNo. 3-2. The tensile strength was significantly improved in No. 3-6containing Cu, Mo and Ti as compared to No. 3-4 containing only Cu andTi and No. 3-5 containing only Mo and Ti. Compared to No. 3-6, a hightensile strength was obtained in No. 3-7 with increased Cu, No. 3-8 withincreased Mo, and No. 3-9 with increased Ti. On the other hand, No.3-10, in which the amounts of Cu, Mo and Ti were outside the range ofthe present disclosure, had a lowered density and a deteriorated tensilestrength.

With regard to compressibility, it can be seen that Nos. 3-2 and 3-6 to3-9, which are disclosed examples, all have a sufficiently high densityand excellent compressibility. It can be seen from the results of Nos.3-5 to 3-7 that Cu can improve the tensile strength by increasing theamount added while maintaining a high density.

The sintered body of No. 3-11 using a diffusionally adhered alloy steelpowder, in which Cu was diffusively adhered to the surface of an alloyedsteel powder containing Mo and Ti as alloying elements, and the sinteredbody of No. 3-12 using a mixed powder obtained by mixing the samealloyed steel powder with a Cu powder were inferior to the sintered bodyof No. 3-6 in terms of tensile strength, although they had the samecontents of Cu, Mo and Ti. The sintered body of No. 3-13 using adiffusionally adhered alloy steel powder, in which Mo was diffusivelyadhered to the surface of an alloyed steel powder containing Cu and Tias alloying elements, and the sintered body of No. 3-14 using a mixedpowder obtained by mixing the same alloyed steel powder with a Mo powderwere inferior to the sintered body of No. 3-6 in terms of tensilestrength, although they had the same contents of Cu, Mo and Ti.

TABLE 3 Metal Alloyed steel Diffusionally powder powder adhered powderAmount Sintered Chemical Amount added*³ Formed body composition *¹adhered*² (mass %) body Tensile (mass %) (mass %) Cu Mo Density strengthNo. Cu Mo Ti Cu Mo powder powder (Mg/m³) (MPa) Remarks 3-1 1.0 — 0.02 —— — — 7.07 455 Comparative example 3-2 1.0 0.51 0.02 — — — — 7.01 567Example 3-3 3.0 0.51 — — — — — 7.00 527 Comparative example 3-4 3.0 —0.10 — — — — 7.04 476 Comparative example 3-5 — 1.20 0.10 — — — — 6.97603 Comparative example 3-6 3.0 1.20 0.10 — — — — 6.90 755 Example 3-78.0 1.20 0.10 — — — — 6.99 751 Example 3-8 3.0 2.00 0.10 — — — — 6.84760 Example 3-9 3.0 1.20 0.40 — — — — 6.82 690 Example 3-10 8.1 2.100.41 — — — — 6.63 614 Comparative example 3-11 — 1.20 0.10 3.0 — — —6.97 604 Comparative example 3-12 — 1.20 0.10 — — 3.0 — 6.98 596Comparative example 3-13 3.0 — 0.10 — 1.20 — — 7.03 509 Comparativeexample 3-14 3.0 — 0.10 — — — 1.20 7.03 504 Comparative example *¹ Thebalance of the alloyed steel powder consists of Fe and inevitableimpunties. *²The total of the alloyed steel powder and the diffusionallyadhered powder is taken as 100 mass %. *³The total of the alloyed steelpowder and the metal powder is taken as 100 mass %.

Example 4

This is an example relating to an alloyed steel powder in which Cu, Mo,and two or three selected from V, Nb and Ti are added as alloycomponents. Table 4 lists the chemical composition and the evaluationresults.

According to Nos. 4-1 to 4-3, 4-5 to 4-7, 4-9 to 4-11 and 4-13 to 4-15,it can be seen that the tensile strength is further improved by using analloyed steel powder in which two or three selected from V, Ni and Tiwere added in specific amounts. Further, all of these examples had asufficiently high density and excellent compressibility. On the otherhand, the tensile strength decreased in Nos. 4-4, 4-8, 4-12 and 4-16where the amount added did not meet the specified conditions.

TABLE 4 Sintered Formed body Alloyed steel powder body Tensile Chemicalcomposition * (mass %) Density strength No. Cu Mo V Nb Ti (Mg/m³) (MPa)Remarks 4-1 3.0 1.20 0.20 0.02 — 6.93 794 Example 4-2 3.0 1.20 0.20 0.10— 6.93 807 Example 4-3 3.0 1.20 0.20 0.40 — 6.89 784 Example 4-4 3.01.20 0.20 0.50 — 6.89 725 Comparative example 4-5 3.0 1.20 0.20 — 0.026.92 805 Example 4-6 3.0 1.20 0.20 — 0.10 6.92 806 Example 4-7 3.0 1.200.20 — 0.40 6.89 789 Example 4-8 3.0 1.20 0.20 — 0.50 6.89 734Comparative example 4-9 3.0 1.20 — 0.10 0.02 6.94 797 Example 4-10 3.01.20 — 0.10 0.10 6.94 806 Example 4-11 3.0 1.20 — 0.10 0.40 6.91 781Example 4-12 3.0 1.20 — 0.10 0.50 6.91 727 Comparative example 4-13 3.01.20 0.20 0.02 0.02 6.90 801 Example 4-14 3.0 1.20 0.20 0.10 0.10 6.89812 Example 4-15 3.0 1.20 0.20 0.40 0.40 6.88 777 Example 4-16 3.0 1.200.20 0.50 0.50 6.88 659 Comparative example * The balance consists of Feand inevitable impurities.

Example 5

This is an example relating to a mixed powder in which a Cu powderand/or a Mo powder is further added to an alloyed steel powder. Table 5lists the amounts of the alloyed steel powder, Cu powder and Mo powderadded, as well as the evaluation results.

Comparing No. 1-6 with Nos. 5-1, 5-3 to 5-4, and 5-6, comparing No. 2-6with Nos. 5-8, 5-10 to 5-11, and 5-13, comparing No. 3-6 with Nos. 5-15,5-17 to 5-18, and 5-20, comparing No. 4-10 with Nos. 5-22, 5-24 to 5-25,and 5-27, and comparing No. 4-14 with Nos. 5-29, 5-31 to 5-32, and 5-34,it can be seen that the tensile strength is further improved by mixing aCu powder and/or a Mo powder in a specific amount. Further, all of theseexamples had a sufficiently high density and excellent compressibility.On the other hand, the tensile strength was decreased in Nos. 5-2, 5-5,5-7, 5-9, 5-12, 5-14, 5-16, 5-19, 5-21, 5-23, 5-26, 5-28, 5-30, 5-33 and5-35 where the amount of Cu powder and/or Mo powder added did not meetthe specified conditions.

TABLE 5 Mixed powder Sintered Amount added* Formed body (mass %) bodyTensile Alloyed steel Cu Mo Density strength No. powder powder powder(Mg/m³) (MPa) Remarks 1-6 No.1-6 — — 6.91 770 Example 5-1 4 — 6.86 838Example 5-2 5 — 6.83 763 Comparative example 5-3 — 2 6.85 825 Example5-4 — 4 6.80 830 Example 5-5 — 5 6.75 764 Comparative example 5-6 4 46.76 855 Example 5-7 5 5 6.66 724 Comparative example 2-6 No.2-6 — —6.92 763 Example 5-8 4 — 6.87 830 Example 5-9 5 — 6.84 755 Comparativeexample 5-10 — 2 6.86 817 Example 5-11 — 4 6.81 822 Example 5-12 — 56.76 757 Comparative example 5-13 4 4 6.77 847 Example 5-14 5 5 6.66 715Comparative example 3-6 No.3-6 — — 6.90 755 Example 5-15 4 — 6.87 822Example 5-16 5 — 6.84 747 Comparative example 5-17 — 2 6.86 809 Example5-18 — 4 6.81 814 Example 5-19 — 5 6.76 749 Comparative example 5-20 4 46.77 839 Example 5-21 5 5 6.66 708 Comparative example 4-10 No.4-10 — —6.94 806 Example 5-22 4 — 6.89 861 Example 5-23 5 — 6.88 790 Comparativeexample 5-24 — 2 6.88 850 Example 5-25 — 4 6.83 854 Example 5-26 — 56.80 811 Comparative example 5-27 4 4 6.79 885 Example 5-28 5 5 6.75 755Comparative example 4-14 No.4-14 — — 6.89 812 Example 5-29 4 — 6.85 868Example 5-30 5 — 6.84 796 Comparative example 5-31 — 2 6.84 856 Example5-32 — 4 6.79 861 Example 5-33 — 5 6.77 810 Comparative example 5-34 4 46.75 891 Example 5-35 5 5 6.72 762 Comparative example *³The mixedpowder is taken as 100 mass %.

1. An alloyed steel powder for powder metallurgy, comprising Cu: 1.0mass % or more and 8.0 mass % or less, Mo: more than 0.50 mass % and2.00 mass % or less, and at least one selected from the group consistingof V: 0.05 mass % or more and 0.50 mass % or less, Nb: 0.02 mass % ormore and 0.40 mass % or less, and Ti: 0.02 mass % or more and 0.40 mass% or less, with the balance consisting of Fe and inevitable impurities.2. The alloyed steel powder for powder metallurgy according to claim 1,comprising V: 0.05 mass % or more and 0.50 mass % or less.
 3. Thealloyed steel powder for powder metallurgy according to claim 1,comprising Nb: 0.02 mass % or more and 0.40 mass % or less.
 4. Thealloyed steel powder for powder metallurgy according to claim 1,comprising Ti: 0.02 mass % or more and 0.40 mass % or less.
 5. Aniron-based mixed powder for powder metallurgy, comprising the alloyedsteel powder for powder metallurgy according to claim 1 and a metalpowder, wherein the metal powder is either or both of a Cu powder ofmore than 0 mass % and 4 mass % or less and a Mo powder of more than 0mass % and 4 mass % or less with respect to 100 mass % of the iron-basedmixed powder for powder metallurgy.
 6. A sintered body using the alloyedsteel powder for powder metallurgy according to claim
 1. 7. The alloyedsteel powder for powder metallurgy according to claim 2, comprising Nb:0.02 mass % or more and 0.40 mass % or less.
 8. The alloyed steel powderfor powder metallurgy according to claim 2, comprising Ti: 0.02 mass %or more and 0.40 mass % or less.
 9. The alloyed steel powder for powdermetallurgy according to claim 3, comprising Ti: 0.02 mass % or more and0.40 mass % or less.
 10. The alloyed steel powder for powder metallurgyaccording to claim 7, comprising Ti: 0.02 mass % or more and 0.40 mass %or less.
 11. An iron-based mixed powder for powder metallurgy,comprising the alloyed steel powder for powder metallurgy according toclaim 2 and a metal powder, wherein the metal powder is either or bothof a Cu powder of more than 0 mass % and 4 mass % or less and a Mopowder of more than 0 mass % and 4 mass % or less with respect to 100mass % of the iron-based mixed powder for powder metallurgy.
 12. Aniron-based mixed powder for powder metallurgy, comprising the alloyedsteel powder for powder metallurgy according to claim 3 and a metalpowder, wherein the metal powder is either or both of a Cu powder ofmore than 0 mass % and 4 mass % or less and a Mo powder of more than 0mass % and 4 mass % or less with respect to 100 mass % of the iron-basedmixed powder for powder metallurgy.
 13. An iron-based mixed powder forpowder metallurgy, comprising the alloyed steel powder for powdermetallurgy according to claim 4 and a metal powder, wherein the metalpowder is either or both of a Cu powder of more than 0 mass % and 4 mass% or less and a Mo powder of more than 0 mass % and 4 mass % or lesswith respect to 100 mass % of the iron-based mixed powder for powdermetallurgy.
 14. An iron-based mixed powder for powder metallurgy,comprising the alloyed steel powder for powder metallurgy according toclaim 7 and a metal powder, wherein the metal powder is either or bothof a Cu powder of more than 0 mass % and 4 mass % or less and a Mopowder of more than 0 mass % and 4 mass % or less with respect to 100mass % of the iron-based mixed powder for powder metallurgy.
 15. Aniron-based mixed powder for powder metallurgy, comprising the alloyedsteel powder for powder metallurgy according to claim 8 and a metalpowder, wherein the metal powder is either or both of a Cu powder ofmore than 0 mass % and 4 mass % or less and a Mo powder of more than 0mass % and 4 mass % or less with respect to 100 mass % of the iron-basedmixed powder for powder metallurgy.
 16. An iron-based mixed powder forpowder metallurgy, comprising the alloyed steel powder for powdermetallurgy according to claim 9 and a metal powder, wherein the metalpowder is either or both of a Cu powder of more than 0 mass % and 4 mass% or less and a Mo powder of more than 0 mass % and 4 mass % or lesswith respect to 100 mass % of the iron-based mixed powder for powdermetallurgy.
 17. An iron-based mixed powder for powder metallurgy,comprising the alloyed steel powder for powder metallurgy according toclaim 10 and a metal powder, wherein the metal powder is either or bothof a Cu powder of more than 0 mass % and 4 mass % or less and a Mopowder of more than 0 mass % and 4 mass % or less with respect to 100mass % of the iron-based mixed powder for powder metallurgy.
 18. Asintered body using the iron-base mixed powder for powder metallurgyaccording to claim 5.